CreateObject is known to have collision issues. Over time, certain parts of the collision mesh tend to "disappear". I've looked at this already and it seems to happen around the world sector edges. Collision detection may simply fail over time. I'm 99% sure this is the problem you are facing, and may take several hours to replicate. Sometimes it can indeed appear much sooner, but I haven't managed to get the game to do that consistently.
TLDR: We're still looking into this problem. It has already been reported on the bug tracker numerous times.